Hermaphrodite


Hermaphrodite
Mating Helix aspersa (garden snails).

In biology, a hermaphrodite is an organism that has reproductive organs normally associated with both male and female sexes.[1]

Many taxonomic groups of animals (mostly invertebrates) do not have separate sexes. In these groups, hermaphroditism is a normal condition, enabling a form of sexual reproduction in which both partners can act as the "female" or "male". For example, the great majority of pulmonate snails, opisthobranch snails and slugs are hermaphrodites. Hermaphroditism is also found in some fish species and to a lesser degree in other vertebrates. Most plants are also hermaphrodites.

Historically, the term hermaphrodite has also been used to describe ambiguous genitalia and gonadal mosaicism in individuals of gonochoristic species, especially human beings. The word hermaphrodite entered the English lexicon in the 15th century, derived from the Greek Hermaphroditos a combination of the names of the gods Hermes (male) and Aphrodite (female).[2] Recently, the word "intersex" has come into preferred usage for humans, since the word "hermaphrodite" is considered to be misleading and stigmatizing,[3] and "scientifically specious and clinically problematic."[4]


Contents

Zoology

Sequential hermaphrodites

Shells of Crepidula fornicata (common slipper shell).

Sequential hermaphrodites (dichogamy) occur in species in which the individual is born as one sex, but can later change into the alternate sex.[5] This is in contrast with simultaneous hermaphrodites, in which an individual may possess fully functional male and female gonads. Sequential hermaphroditism is common in fish (particularly teleost fish), many gastropods (such as the common slipper shell), and some flowering plants. While some sequential hermaphrodites can change sex multiple times, most can only change sex once.[citation needed] Sequential hermaphrodism can best be understood in terms of behavioral ecology and evolutionary life history theory, as described in the size-advantage model[6] first proposed by Michael T. Ghiselin[7] which states that if an individual of a certain sex could significantly increase its reproductive success after reaching a certain size, it would be to their advantage to switch to that sex.

Sequential hermaphrodites fall into two broad categories:

  • Protandry: Where an organism is born as a male, and then changes sex to a female.[5]
    • Example: The clownfish (genus Amphiprion) are colorful reef fish found living in symbiosis with sea anemones. Generally one anemone contains a 'harem ', consisting of a large female, a smaller reproductive male, and even smaller non-reproductive males. If the female is removed, the reproductive male will change sex and the largest of the non-re productive males will mature and become reproductive. It has been shown that fishing pressure can change when the switch from male to female occurs, since fishermen usually prefer to catch the larger fish. The populations are generally changing sex at a smaller size, due to natural selection.
  • Protogyny: Where the organism is born as a female, and then changes sex to a male.[5]
    • Example: wrasses (Family Labridae) are a group of reef fish in which protogyny is common. Wrasses also have an uncommon life history strategy, which is termed diandry (literally, two males). In these species, two male morphs exists: an initial phase male or a terminal phase male. Initial phase males do not look like males and spawn in groups with other females. They are not territorial. They are, perhaps, female mimics (which is why they are found swimming in group with other females). Terminal phase males are territorial and have a distinctively bright coloration. Individuals are born as males or females, but if they are born males, they are not born as terminal phase males. Females and initial phase males can become terminal phase males. Usually, the most dominant female or initial phase male replaces any terminal phase male when those males die or abandon the group.

Dichogamy can have both conservation-related implications for humans, as mentioned above, as well as economic implications. For instance, groupers are favoured fish for eating in many Asian countries and are often aquacultured. Since the adults take several years to change from female to male, the broodstock are extremely valuable individuals.

Simultaneous hermaphrodites

Earthworms are simultaneous hermaphrodites, having both male and female reproductive organs.

A simultaneous (or synchronous) hermaphrodite (homogamy) is an adult organism that has both male and female sexual organs at the same time.[5] Usually, self-fertilization does not occur.

  • Reproductive system of gastropods: Pulmonate land snails and land slugs are perhaps the best-known kind of simultaneous hermaphrodite, and are the most widespread of terrestrial animals possessing this sexual polymorphism. Sexual material is exchanged between both animals via spermatophore, which can then be stored in the spermatheca. After exchange of spermatozoa, both animals will lay fertilized eggs after a period of gestation; then the eggs will proceed to hatch after a development period. Snails typically reproduce in early spring and late autumn.
  • Banana slugs are one example of a hermaphroditic gastropod. Mating with a partner is more desirable biologically, as the genetic material of the resultant offspring is varied, but if mating with a partner is not possible, self-fertilization is practiced. The male sexual organ of an adult banana slug is quite large in proportion to its size, as well as compared to the female organ. It is possible for banana slugs, while mating, to become stuck together. If a substantial amount of wiggling fails to separate them, the male organ will be bitten off (using the slug's radula), see apophallation. If a banana slug has lost its male sexual organ, it can still mate as a female, making its hermaphroditic quality a valuable adaptation.
  • Hamlets, unlike other fish, seem quite at ease mating in front of divers, allowing observations in the wild to occur readily. They do not practice self-fertilization, but when they find a mate, the pair takes turns between which one acts as the male and which acts as the female through multiple matings, usually over the course of several nights.
  • Earthworms are another example of a simultaneous hermaphrodite. Although they possess ovaries and testes, they have a protective mechanism against self fertilization. Sexual reproduction occurs when two worms meet and exchange gametes, copulating on damp nights during warm seasons. Fertilized eggs are protected by a cocoon, which is buried on or near the surface of the ground.

Pseudohermaphroditism

When hyenas were first discovered by explorers, they were thought to be hermaphrodites. Observation of packs of hyenas in the wild (in the 1960s) revealed all hyenas, male and female, are born with what appears to be a penis. The two genders are almost impossible to tell apart until they reach sexual maturity and they either have babies or don't. The apparent penis in females is an external birth canal.[8] When the babies are born, they pass through the cervix internally, but then pass into this external canal, which is less muscular than a usual birth canal.[9]

Humans

True hermaphroditism in humans differs from pseudohermaphroditism in which the person has both X and Y chromosomes (not to be confused with the normal XY chromosome of males), having both testicular and ovarian tissue, and having both but ambiguous-looking external genitalia. One possible pathophysiologic explanation of this rare phenomenon is a parthenogentic division of a haploid ovum into two haploid ova. Upon fertilization of the two ova by two sperm cells (one carrying an X and the other carrying a Y chromosome), the two fertilized ova are then fused together resulting in a person having dual genitalial, gonadal and genetic sex.

Botany

Hylocereus undatus, a hermaphrodite plant with both carpels and stamens

Hermaphrodite is used in botany to describe a flower that has both staminate (male, pollen-producing) and carpellate (female, ovule-producing) parts. This condition is seen in many common garden plants. A closer analogy to hermaphroditism in animals is the presence of separate male and female flowers on the same individual—such plants are called monoecious. Monoecy is especially common in conifers, but occurs in only about 7% of angiosperm species.[10]

Other uses of the term

Hermaphroditus, mythological character: origin of the word 'Hermaphrodite'.

Hermaphrodite was used to describe any person incompatible with the biological gender binary, but has recently been replaced by intersex in medicine. Humans with typical reproductive organs but atypical clitoris/penis are called pseudohermaphrodites in medical literature. Pseudohermaphroditism also refers to a human possessing both the clitoris and testicles.[11]

People with intersex conditions sometimes choose to live exclusively as one sex or the other, using clothing, social cues, genital surgery, and hormone replacement therapy to blend into the sex they identify with more closely. Some people who are intersex, such as some of those with androgen insensitivity syndrome, outwardly appear completely female or male already, without realizing they are intersex. Other kinds of intersex conditions are identified immediately at birth because those with the condition have a sexual organ larger than a clitoris and smaller than a penis. Intersex is thought by some to be caused by unusual sex hormones; the unusual hormones may be caused by an atypical set of sex chromosomes.

Sigmund Freud (based on work by his associate Wilhelm Fliess) held fetal hermaphroditism to be a fact of the physiological development of humans.[citation needed] He based much of his theory of innate sexuality on that assumption.[citation needed] Similarly, in contemporary times, fetuses before sexual differentiation are sometimes described as female by doctors explaining the process.[12] Neither concept is technically true. Before this stage, humans are simply undifferentiated and possess a Müllerian duct, a Wolffian duct, and a genital tubercle.

Etymology

The term "hermaphrodite" derives from Hermaphroditus, the son of Hermes and Aphrodite in Greek mythology, who was fused with a nymph, Salmacis, resulting in one individual possessing physical traits of both sexes.[13]

See also

References

  1. ^ Merriam-Webster Dictionary Retrieved 28 June 2011
  2. ^ Word origin and history: Hermaphrodite Word-Origins.com
  3. ^ "Is a person who is intersex a hermaphrodite?". Intersex Society of North America. http://www.isna.org/faq/hermaphrodite. Retrieved 2 October 2011. 
  4. ^ Herndon, April. "Getting Rid of "Hermaphroditism" Once and For All". Intersex Society of North America. http://www.isna.org/node/979. Retrieved 2 October 2011. 
  5. ^ a b c d Barrows, Edward M. (2001). Animal behavior desk reference: a dictionary of animal behavior, ecology, and evolution (2nd ed.). Boca Raton, Fla: CRC Press. p. 317. ISBN 0849320054. OCLC 299866547. 
  6. ^ Warner, Robert R (June 1988). "Sex change and the size-advantage model". Trends in Ecology and Evolution 3 (6): 133–136. doi:10.1016/0169-5347(88)90176-0. PMID 21227182. 
  7. ^ Ghiselin, Micahel T. (1969). "The evolution of hermaphroditism among animals". Quarterly Review of Biology 44 (2): 189–208. doi:10.1086/406066. PMID 4901396. 
  8. ^ Graphic depiction of female hyena's reproductive system
  9. ^ Hermaphrodite Hyenas? - Animal Life by MaryEllen Schoeman
  10. ^ Molnar, Sebastian (17 February 2004). "Plant Reproductive Systems". Evolution and the Origins of Life. Geocities.com. Archived from the original on 2009-10-22. http://web.archive.org/web/20091022174814/http://geocities.com/we_evolve/Plants/breeding_sys.html. Retrieved 12 September 2009. 
  11. ^ Voss, Heinz-Juergen: Sex In The Making - A Biological Account. Online: http://DasEndeDesSex.blogsport.de/images/voss_2011_sex_in_the_making.pdf
  12. ^ Leyner, Mark; Goldberg M.D., Billy (2005). Why Do Men Have Nipples?: Hundreds of Questions You'd Only Ask a Doctor After Your Third Martini. New York: Three Rivers Press. ISBN 1400082315. OCLC 57722472. 
  13. ^ Ovid, Metamorphoses, Book IV: The story of Hermaphroditus and Salmacis.

Further reading

External links


Wikimedia Foundation. 2010.

Synonyms:

Look at other dictionaries:

  • HERMAPHRODITE — L’enjeu philosophique du symbolisme de l’hermaphrodite est tout entier présent dans un aphorisme de l’alchimiste Heinrich C. Khunrath: «De l’Un grossier et impur naît un Un extrêmement pur et subtil.» L’hermaphrodite symbolise le processus de… …   Encyclopédie Universelle

  • hermaphrodite — HERMAPHRODITE. s. m. Celuy qui a les deux sexes. Un Hermaphrodite. on dit que les hermaphrodites sont communs en certains pays. Il est aussi adj. des deux genres. Une femme hermaphrodite. il est hermaphrodite …   Dictionnaire de l'Académie française

  • Hermaphrodite — Her*maph ro*dite, a. Including, or being of, both sexes; as, an hermaphrodite animal or flower. [1913 Webster] {Hermaphrodite brig}. (Naut.) See under {Brig}. Totten …   The Collaborative International Dictionary of English

  • Hermaphrodite — Her*maph ro*dite, n. [L. hermaphroditus, Gr. ?, so called from the mythical story that Hermaphroditus, son of Hermes and Aphrodite, when bathing, became joined in one body with Salmacis, the nymph of a fountain in Caria: cf. F. hermaphrodite.]… …   The Collaborative International Dictionary of English

  • hermaphrodite — [hər maf′rə dīt΄] n. [altered (modeled on L or Gr) < ME hermofrodite < L hermaphroditus < Gr hermaphroditos, < Hermaphroditos, HERMAPHRODITUS] 1. a person or animal with the sexual organs of both the male and the female 2. a plant… …   English World dictionary

  • hermaphrodite — hermaphrodite. См. гермафродит. (Источник: «Англо русский толковый словарь генетических терминов». Арефьев В.А., Лисовенко Л.А., Москва: Изд во ВНИРО, 1995 г.) …   Молекулярная биология и генетика. Толковый словарь.

  • hermaphrodite — HERMAPHRODITE: Excite la curiosité malsaine. Chercher à en voir …   Dictionnaire des idées reçues

  • hermaphrodite — late 14c. (harmofroditus), from L. hermaphroditus, from Gk. Hermaphroditos (L. Hermaphroditus), son of Hermes and Aphrodite, who, in Ovid, was loved by the nymph Salmacis so ardently that she prayed for complete union with him and as a result… …   Etymology dictionary

  • hermaphrodite — ► NOUN 1) a person or animal having both male and female sex organs or other sexual characteristics. 2) Botany a plant having stamens and pistils in the same flower. DERIVATIVES hermaphroditic adjective hermaphroditism noun. ORIGIN Greek… …   English terms dictionary

  • Hermaphrodite — Pour les articles homonymes, voir Hermaphrodite (homonymie). Hermaphrodite endormi, copie romaine d un original grec, époque impériale (II …   Wikipédia en Français


Share the article and excerpts

Direct link
Do a right-click on the link above
and select “Copy Link”

We are using cookies for the best presentation of our site. Continuing to use this site, you agree with this.